The present invention relates to a reactive agent and a process for decomposing and detoxifying various fluorine compounds such as chlorofluorocarbons (hereinafter simply referred to as xe2x80x9cCFCxe2x80x9d), hydrochlorofluorocarbons (hereinafter simply referred to as xe2x80x9cHCFCxe2x80x9d), perfluorocarbons (hereinafter simply referred to as xe2x80x9cPFCxe2x80x9d), hydrofluoro-carbons (hereinafter simply referred to as xe2x80x9cHFCxe2x80x9d), perfluoroethers (hereinafter simply referred to as xe2x80x9cPFExe2x80x9d), hydrofluoroethers (hereinafter simply referred to as xe2x80x9cHFExe2x80x9d) and sulfur fluoride, simultaneously with the compounds produced on using these fluorine compounds, for example, in an etching or cleaning step during the process of manufacturing a semiconductor device, such as HF, SiF4 or COF2.
Most of the above-described fluorine compounds are generally stable and harmless to the human body, therefore, their use is outspread in various fields. In recent years, the amount of HFC as a refrigerant of car air conditioner or the like and PFC for etching or as a cleaning gas in the process of manufacturing semiconductors is particularly increased. Furthermore, a large amount of sulfur hexafluoride is being used for capacitors, transformers and the like because of its excellent electrical insulating property. These fluorine compounds are a stable compound and in turn have a large global warming potential coefficient. If such a fluorine compound is released as it is into the global environment, there is a fear that its effect continues for a long period of time. In particular, SF6, CF4, C2F6 and the like are a very stable gas and have a very long life in air. Therefore, on discharge after their use, these gases must be released after decomposition into a harmless substance having no effect on the global environment. As an alternate compound therefor, PFE and HFE are proposed but these also have the same global warming problem. Furthermore, the gas discharged after use in the process of manufacturing semiconductor devices contains gases such as HF, SiF4 and COF2 and these gases must also be released after decomposition into a safe substance together with the above-described compounds.
CFC heretofore used in a large amount as a refrigerant, detergent or the like, and HCFC as an alternate compound thereof cannot be released as it is and must be decomposed into a harmless substance because ozone layer destruction occurs as a serious environmental problem.
Conventionally, as a technique for decomposing such fluorine compounds, for example, (1) a combustion decomposition method of treating the compound together with a fuel (see, WO94/05399), (2) a thermal decomposition method using a reactive agent such as silica or zeolite (see, JP-A-7-116466 (the term xe2x80x9cJP-Axe2x80x9d as used herein means an xe2x80x9cunexamined published Japanese patent applicationxe2x80x9d)), and (3) a catalytic decomposition method using an alumina or the like (see, JP-A-10-286434) are known.
However, method (1) is disadvantageous in that generation of NOx must be controlled during the combustion or a large amount of diluting gas is necessary, causing a decrease in the decomposing ratio, and moreover, a secondary treatment of HF contained in the exhaust gas after the decomposition is necessary. Method (2) also has a problem in that a high temperature of 1,000xc2x0 C. or more is necessary particularly for decomposing PFC (e.g., CF4, C2F6) at a sufficiently high rate and moreover, a separate secondary treatment of compounds such as SiF4 contained in the exhaust gas after the decomposition is necessary. According to the method (3), decomposition may be performed at a relatively low temperature as compared with the methods (1) and (2), however, the following problems still remain. For decomposing PFC in an amount of 100%, the supply gas must be diluted with air or the like to reduce the PFC concentration in the gas. Furthermore, in order to bring out the catalytic action of alumina, it is necessary to allow a large amount of steam to be present together and thereby hydrolyze, for example, fluoride or the like accumulated on the alumina surface. Therefore, an anticorrosive material against HF generated by the high-temperature decomposition of fluoride on the alumina surface, and a secondary treatment of HF are necessary.
As such, a method for effectively decomposing fluorine compounds using an industrially advantageous process is heretofore not known and more improvements are demanded.
An object of the present invention is to solve the above-described problems and provide a reactive agent which can thermally decompose fluorine compounds at a relatively low temperature without adding water and which can fix the decomposition products (e.g., F, SOx) of the decomposed fluorine compound to the reactive agent.
Another object of the present invention is to provide a process for efficiently decomposing particularly PFC which is difficult to decompose.
As a result of extensive investigations to solve the above-described problems, the present inventors have found that these objects can be attained by a reactive agent for decomposing fluorine compounds, comprising alumina and an alkaline earth metal compound. Furthermore, the present inventors have found that in a process for decomposing fluorine compounds, comprising contacting a fluorine compound with the above-described reactive agent at a temperature of 200xc2x0 C. or more, the fluorine compound can be thermally decomposed, the generated chlorine atoms, fluorine atoms and/or sulfur atoms can be fixed as a chloride, a fluoride and/or a sulfate of an alkaline earth metal in the reactive agent, and if desired, by adding a metal oxide to the reactive agent to incorporate oxygen into the fluorine compound, the carbon monoxide generated can be simultaneously oxidized and thereby detoxified. The present invention has been accomplished based on these findings. The present invention relates to a reactive agent and a process for decomposing fluorine compounds, described in (1) to (28) below:
(1) A reactive agent for decomposing fluorine compounds, comprising alumina and an alkaline earth metal compound;
(2) the reactive agent for decomposing fluorine compounds as described in (1) above, wherein the alumina has a specific surface area of 50 m2/g or more;
(3) the reactive agent for decomposing fluorine compounds as described in (1) or (2) above, wherein the alumina is pseudo boehmite alumina;
(4) the reactive agent for decomposing fluorine compounds as described in (1) or (2) above, wherein the alumina is obtained by baking pseudo boehmite alumina at a baking temperature of from h400 to 1,000xc2x0 C.;
(5) the reactive agent for decomposing fluorine compounds as described in any one of (1) to (4) above, wherein the alkaline earth metal compound is a carbonate of magnesium, calcium, strontium or barium;
(6) the reactive agent for decomposing fluorine compounds as described in any one of (1) to (5) above, wherein the alumina and the alkaline earth metal compound present in the reactive agent each is in the form of a powder having a particle size of 100 xcexcm or less;
(7) the reactive agent for decomposing fluorine compounds as described in any one of (1) to (6) above, wherein the alumina and the alkaline earth metal compound are present in the reactive agent at a mass ratio of from 1:9 to 1:1;
(8) the reactive agent for decomposing fluorine compounds as described in any one of (1) to (7) above, which contains at least one oxide of a metal selected from the group consisting of copper, tin, nickel, cobalt, chromium, molybdenum, tungsten and vanadium;
(9) the reactive agent for decomposing fluorine compounds as described in (8) above, wherein the content of the metal oxide is, in terms of a ratio to the total mass of the alumina and alkaline earth metal compound, from 1:99 to 5:95;
(10) the reactive agent for decomposing fluorine compounds as described in any one of (1) to (9), which has an alkali metal content of 0.1 mass % or less;
(11) the reactive agent for decomposing fluorine compounds as described in any one of (1) to (10) above, which is a granular product obtained by baking at a temperature of from 400 to 700xc2x0 C.;
(12) the reactive agent for decomposing fluorine compounds as described in (11) above, which is a granular product having a particle size of from 0.5 to 10 mm;
(13) the reactive agent for decomposing fluorine compounds as described in any one of (1) to (12) above, which has a water content of 1 mass % or less.
(14) the reactive agent for decomposing fluorine compounds as described in any one of (1) to (13) above, wherein the fluorine compound is at least one fluorine compound selected from the group consisting of perfluorocarbon, hydrofluorocarbon, chlorofluorocarbon, hydrochlorofluorocarbon, perfluoroether, hydrofluoroether, fluoroolefin, sulfur fluoride, SiF4 and COF2;
(15) the reactive agent for decomposing fluorine compounds as described in (14) above, wherein the fluorine compound contains hydrogen chloride and/or hydrogen fluoride;
(16) a process for decomposing fluorine compounds, comprising contacting a reactive agent described in any one of (1) to (15) above with a fluorine compound at a temperature of 200xc2x0 C. or more;
(17) the process for decomposing fluorine compounds as described in (16) above, wherein the fluorine compound concentration in a gas to be treated by contacting it with a reactive agent described in any one of (1) to (15) above is from 0.01 to 10 vol %;
(18) a process for decomposing fluorine compounds, comprising contacting a reactive agent described in any one of (1) to (15) above with a fluorine compound at a temperature of 500xc2x0 C. or more in the presence of oxygen gas, thereby controlling the generation of carbon monoxide;
(19) the process for decomposing fluorine compounds as described in (18) above, wherein the oxygen gas concentration in a gas to be treated is 20 vol % or less;
(20) the process for decomposing fluorine compounds as described in any one of (16) to (19) above, wherein chlorine atom, fluorine atom and/or sulfur atom produced on contacting a reactive agent described in any one of (1) to (15) above with a fluorine compound are fixed as an alkaline earth metal chloride, an alkaline earth metal fluoride and/or an alkaline earth metal sulfate, respectively;
(21) a process for manufacturing a semiconductor device, comprising an etching or cleaning step of using as an etching gas or cleaning gas at least one fluorine compound selected from the group consisting of perfluorocarbon, hydrofluorocarbon, chlorofluorocarbon, hydrochlorofluorocarbon, perfluoroether, hydrofluoroether, fluoroolefin and sulfur fluoride, and a decomposition step of decomposing the fluorine compound-containing gas discharged from the etching or cleaning step using a reactive agent described in any one of (1) to (15) above;
(22) the process for manufacturing a semiconductor device as described in (21) above, wherein the gas discharged from the etching or cleaning step is a gas containing at least one fluorine compound selected from the group consisting of perfluorocarbon, hydrofluorocarbon, chlorofluorocarbon, hydrochlorofluorocarbon, perfluoroether, hydrofluoroether, fluoroolefin, sulfur fluoride, SiF, and COF2;
(23) the process for manufacturing a semiconductor device as described in (22) above, wherein the fluorine compound-containing gas contains hydrogen chloride and/or hydrogen fluoride;
(24) the process for manufacturing a semiconductor device as described in any one of (21) to (23) above, wherein in the decomposition step, the fluorine compound in a gas to be treated is decomposed at a temperature of 200xc2x0 C. or more;
(25) the process for manufacturing a semiconductor device as described in any one of (21) to (24) above, wherein in the decomposition step, the fluorine compound concentration in a gas to be treated is from 0.01 to 10 vol %;
(26) a process for manufacturing a semiconductor device comprising the decomposition step is performed at a temperature of 500xc2x0 C. or more in the presence of oxygen gas, thereby controlling the generation of carbon monoxide;
(27) the process for manufacturing a semiconductor device as described in (26) above, wherein in the decomposition step, the oxygen gas concentration in a gas to be treated is 20 vol % or less;
(28) the process for manufacturing a semiconductor device as described in any one of (21) to (27) above, wherein chlorine atom, fluorine atom and/or sulfur atom produced in the decomposition step of decomposing the gas discharged from the etching or cleaning step using a reactive agent described in any one of (1) to (15) above are fixed as an alkaline earth metal chloride, an alkaline earth metal fluoride and/or an alkaline earth metal sulfate, respectively.
In summary, the present invention provides xe2x80x9ca reactive agent for decomposing fluorine compounds, comprising alumina and an alkaline earth metal compound, which can decompose and detoxify fluorine compounds having a high ozone layer destruction coefficient or a high global warming potential coefficientxe2x80x9d, xe2x80x9ca process for decomposing fluorine compounds, comprising contacting a fluorine compound with the above-described reactive agent at a temperature of 200xc2x0 C. or morexe2x80x9d, xe2x80x9ca process for decomposing fluorine compounds, comprising incorporating oxygen into a fluorine compound and contacting the fluorine compound with the above-described reactive agent at a temperature of 500xc2x0 C. or more, thereby controlling the generation of carbon monoxidexe2x80x9d, and xe2x80x9ca process for manufacturing a semiconductor device, comprising an etching or cleaning step and a decomposition step of decomposing a gas containing fluorine compounds discharged from the etching or cleaning step using the above-described reacting agentxe2x80x9d.
According to the above-described conventional techniques, namely, (1) a combustion decomposition method, (2) a thermal decomposition method using a reactive agent and (3) a decomposition method using an alumina catalyst, the decomposition product of fluorine compounds is a substance still having harmful effect on the environment. Therefore, a treatment for detoxifying the decomposition product must be separately employed in the later stage of the decomposition step. This makes it difficult to downsize the apparatus. In particular, the gases discharged from the manufacturing process of semiconductor devices, for example, PFC exhaust gas used for etching or cleaning contains fluorine compounds such as HF, SiF4 and COF2 in addition to PFC. Accordingly, in the case of the catalytic decomposition method, a treatment for the detoxification of SiF4 and the like is necessary also in the early stage and a complicated and cumbersome apparatus is required. Furthermore, for the decomposition of PFC which is particularly difficult to decompose, a high temperature is necessary but this gives rise to a problem that the material of which the reactor is constructed deteriorates.
On the other hand, according to the present invention, a fluorine compound used for the purpose of electrical insulation, as a refrigerant or in the process of manufacturing semiconductor devices can be efficiently decomposed at a low temperature. In the present invention, the fluorine compound is decomposed simultaneously with SiF4 and the like generated when the fluorine compound is used, for example, in etching. Furthermore, a reaction for fixing and thereby detoxifying, for example, fluorine generated by the decomposition as an alkaline earth metal fluoride (for example, as CaF2) proceeds at the same time. Therefore, the problems in this concern can also be solved.